This invention relates to evaporative emission control systems for internal combustion engines, and more particularly, to a canister purge valve having a pick coil and a release coil which interact with a permanent magnet to selectively open and close a valve element.
Motor vehicles having an internal combustion engine typically include an evaporative emission control system which serves to reduce fuel vapor emissions. Such systems include a vapor collection canister having carbon or other similar material which serves to absorb fuel vapors that are generated within a fuel system. A canister purge valve is located between the canister and an engine intake manifold. The canister purge valve may be opened or closed to either place the canister in fluid communication with the engine intake manifold or to isolate the canister from the engine intake manifold, respectively.
Under the appropriate conditions, the canister is purged so that fuel vapors collected within the canister do not undesirably escape into the atmosphere. This is done by opening the canister purge valve, thus enabling vacuum which is present at the engine intake manifold to draw out the fuel vapors from the canister. The fuel vapors are then used in the normal combustion process.
The canister purge valve typically includes a valve that is actuated by a solenoid having an armature and a stator. One method of opening or latching the valve is to use a coil to generate a magnetic field so as to cause the armature to magnetically xe2x80x9cstickxe2x80x9d to the stator. In order to release the armature, an opposing magnetic force is applied to the stator, which causes the stator to repel the armature to thus close the valve. This is typically done by reversing polarity on the coil through the use of a driver circuit known as an xe2x80x9cHxe2x80x9d driver. However, the use of such drivers increases costs and complexity.
The invention is directed to a solenoid for use in a canister purge valve. The valve includes a housing having an inlet port and an outlet port. The housing further includes a guide element having a bobbin section. A valve shaft is slidably mounted to the guide element, wherein the valve shaft includes a permanent magnet and a valve element. The valve element is movable between a closed position wherein the inlet port is closed and an open position wherein the inlet port is opened. A pick coil is formed on the bobbin adjacent the magnet. The pick coil generates a first magnetic field having a polarity that is oriented to cause a magnetic attraction with the magnet to move the magnet and thus the valve element to the open position. In addition, a release coil is formed on the bobbin adjacent to the magnet, wherein the release coil generates a second magnetic field having a polarity that is oriented to cause the magnet to be repelled to move the magnet and thus the valve element to the closed position.
The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, may be best understood by reference to the following description taken in conjunction with accompanying drawings.